1. Field of the Invention
The present invention generally relates to an electro-optical assembly for image projection, especially in a portable instrument for projecting an image by controlling a light beam using components employed by readers for electro-optically reading indicia, such as a bar code symbol, a signature, or an image.
2. Description of the Related Art
Various optical scanning systems and readers have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a pattern of graphic indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting characteristics. The readers function by electro-optically transforming the spatial pattern represented by the graphic indicia into a time-varying electrical signal which is, in turn, decoded into data which represent the information or characters encoded in the indicia that are intended to be descriptive of the article or some characteristic thereof. Such data is typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control, distribution, transportation and logistics, and the like.
A variety of scanning systems and readers is known. The scanner could be a wand type reader, such as shown in U.S. Pat. No. 5,508,504, herein incorporated by reference, including an emitter and a detector fixedly mounted in a wand, in which case a user holds and manually moves the wand across the symbol. As the wand passes over the bar code symbol, the emitter and associated optics produce a light spot on the symbol, and the detector senses the light reflected back from the symbol as the light spot passes over the bars and spaces of the symbol.
As illustrated in FIG. 1, a bar code symbol 2 consists of a series of light and dark regions 4, 6 typically in the form of rectangles. The widths of the dark regions 6, the bars, and/or the widths of the light regions 4, the spaces, between the bars indicate the encoded information. A specified number and arrangement of these regions represent a character. Standardized encoding schemes specify the arrangements for each character, the acceptable widths and spacings of the regions, the number of characters a symbol may contain or whether symbol length is variable, etc. The known symbologies include, for example, UPC/EAN, Code 128, Codabar, and Interleaved 2 of 5.
To decode a bar code symbol and extract a legitimate message, a bar code reader illuminates the symbol and senses the light reflected therefrom to detect the widths of the bars and the spaces and produces an electrical signal corresponding to the scanned symbol. This electrical signal is decoded to provide multiple alphanumerical characters which are descriptive of the article to which the symbol is attached or to some characteristic thereof.
The known wand-type reader 8 of FIG. 1 contains an emitter 12 and a detector 14, and the user manually moves the wand across the bar code symbol. The detector 14 senses the light reflected from a spot scanned by the wand 8 across the bar code symbol 2, and produces an electrical signal representing the encoded information to a processor 16. Wands have been disclosed, for example, in U.S. Pat. Nos. 4,654,482, 4,907,264 and 4,937,853.
U.S. Pat. No. 4,471,218 discloses a data wand and a data well, and is incorporated herein by reference. According to this patent, a wand-type data entry terminal is entirely self-contained and cordless, and includes reading and storage circuitry. The terminal further allows downloading of data using an optically coupled link. Preferably, the stored data is output using a pulsed beam from the reading beam light source. The output beam is detected by an optical detector and decoded appropriately.
The disclosures of the above mentioned patents are incorporated herein by reference. The general features of construction and operation of a wand-type reader will be apparent to the skilled reader.
According to another system described in U.S. patent application Ser. No. 08/691,263, filed Aug. 2, 1996, commonly assigned herewith, a hand-held optical reader terminal is provided having an ergonomic design. According to that system, there is provided, inter alia, a hand-held optical reader arranged to fit in the hand of a user and including a reader component and a downloading component. The device can include a display screen for displaying control messages or video images, a keypad for inputting control or other data, and a wireless communication link for downloading data read by the reader component to an external device. The system can further include a plurality of interchangeable data collection modules connectable to the main body of the device, each module fulfilling a different function such as image/video capture, audio capture and so forth. As a result, a simple multi-media module is provided.
It is desired, however, to arrive at a lightweight hand-held data reader having a yet wider range of capabilities. In view of the relative simplicity, availability and adaptability of information systems including bar code symbol data storage capability, it is desirable to develop systems particularly suitable for consumer applications.
Alternatively, an optical moving spot scanner sweeps a light beam, such as a laser beam, across the symbol; and a detector senses reflected light from the beam spot swept across the symbol. In each case, the detector produces an analog scan signal representing the encoded information.
Moving spot scanners of this general type have been disclosed for example, in U.S. Pat. Nos. 4,387,297; 4,409,470; 4,760,248; 4,896,026; 5,015,833; 5,262,627; 5,504,316 and 5,625,483, all of which have been assigned to the same assignee as the instant application and each of which is hereby incorporated by reference. Also incorporated by reference herein are U.S. patent application Ser. No. 09/065,867, filed Apr. 24, 1998 and U.S. patent application Ser. No. 08/353,682, filed Dec. 9, 1994, both of which have been assigned to the same assignee as the instant application. As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand-held, portable laser scanning device supported by a user, which is configured to allow the user to aim the scanning head of the device, and more particularly, a light beam, at a targeted symbol to be read, as described below in connection with FIG. 1A.
The light source in a laser scanner bar code reader is typically a semiconductor laser. The use of semiconductor devices as the light source is especially desirable because of their small size, low cost and low voltage requirements. The laser beam is optically modified, typically by an optical assembly, to form a beam spot of a certain size at a target distance. It is often preferred that the cross section of the beam spot measured in the scanning direction at the target distance be approximately the same as the minimum width in the scanning direction between regions of different light reflectivity, i.e., the bars and spaces of the symbol. Although typical readers utilize a single laser source, other bar code readers have been proposed with two or more light sources of different characteristics, e.g., different frequencies.
In the laser beam scanning systems known in the art, a single laser light beam is directed by a lens or other optical components along a light path toward a bar code symbol on a surface. The moving-beam scanner operates by repetitively scanning the light beam in a line or series of lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the pattern of the symbol, or scan a field of view of a photodetector, or do both. The laser beam may be moved by optical or opto-mechanical means to produce a scanning light beam. Such action may be performed by either deflecting the beam (such as by a moving optical element, such as a mirror) or moving the light source itself. U.S. Pat. No. 5,486,944 describes a scanning module in which a mirror is mounted on a flex element for reciprocal oscillation by electromagnetic actuation. U.S. Pat. No. 5,144,120 to Krichever, et al., describes laser, optical and sensor components mounted on a drive for repetitive reciprocating motion either about an axis or in a plane to effect scanning of the laser beam.
Because of the size and optical and electronic complexity of scanning systems and bar code readers, they generally have heretofore not been combined with other devices in the same housing. The conventional use of a liquid crystal display (LCD) with an adequate viewing size on such readers occupies a large physical area and limits any proposed reduction in size for a hand-held system. The display image is displayed in a single color.
Also known in the art, for example, in U.S. Pat. No. 5,617,304, is a laser pointer which is a device that projects a monochromatic spot of light on a target, such as a presentation being made by a lecturer to an audience. The pointer is essentially a flashlight-type device and is usually packaged in a tubular housing.
Scanning systems for writing or printing indicia have been disclosed, for example, in U.S. Pat. Nos. 4,085,423 and 4,908,813. The use of thermally sensitive paper, or utilizing dyes which are sensitive to radiation in a particular frequency spectrum, is known for use in printing systems, such as exemplified in U.S. Pat. No. 5,014,072.
Accordingly, it is a general object of this invention to provide a novel electro-optical display, especially of miniature size, for projecting an image of light on a viewing surface.
More particularly, it is an object of the present invention to provide a compact display alternative to liquid crystal display devices, especially in hand-held instruments.
It is yet another object of the present invention to display human-readable information, especially alphanumerical characters, on or off a portable instrument.
A still further object of the present invention is to provide a compact display module useful in many instruments of different form factors.
Still another object of the present invention is to display an image larger than the instrument that contains the assembly for projecting the image.
It is yet still another object of the present invention to provide a display having a wide viewing angle from all directions with high contrast and reduced glare.
A concomitant object of the present invention is to provide an image projector that consumes little electrical power.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention generally relates to an arrangement for projecting an image for display. The arrangement includes an energizable, electro-optical assembly including a laser for directing a visible light beam toward a viewing surface when energized, and a scanner for sweeping the light beam along a plurality of scan lines or light paths that extend over the viewing surface; and a controller operatively connected to, and operative for energizing, the laser at selected positions of the light beam on at least one of the scan lines to generate individual light pixels at the selected positions, and at a refresh rate at which the pixels persist to enable a human eye to steadily view the image on the viewing surface.
Preferably, the controller is operative for energizing and de-energizing the laser as the light beam is swept along said at least one of the scan lines. The assembly may include additional light sources for generating additional light beams, all of the light beams having different or the same wavelengths.
The assembly further includes a first scan mirror for sweeping the light beam along a first direction along said at least one of the scan lines, and a second scan mirror for sweeping the light beam along a second direction generally orthogonal to the first direction. The controller is operative for energizing and de-energizing the light source as the light beam is swept along a plurality of each of the scan lines.
In a preferred embodiment, a housing is used for supporting the assembly. The housing has a light-transmissive element through which the swept light beam is directed toward the viewing surface. The housing preferably has a size and a shape configured to be held in a user""s hand like a personal digital assistant, or can be mounted around one""s wrist like a watch, or the housing may be elongated and extend between opposite end regions in a pen-like configuration. In another example, the housing may have a panel having a front surface to which the swept light beam is directed. The panel may be mounted on the housing for movement to a display position in which the swept light beam is incident on the front surface of the panel.
In another example, the housing has a screen having a rear surface to which the light beam is directed. The screen preferably has an optically diffusive property and is movable to a deployed position in which the swept light beam is incident on the rear surface of the screen and is diffused through the screen to render the image visible on a front surface of the screen. It is also desirable if the screen has a wavelength filtering function to suppress ambient light and increase display contrast.
It is especially advantageous if the first scan mirror is moved at a first rate of speed through a first angular distance, and if the second scan mirror is moved at a second rate of speed slower than said first speed, and through a second angular distance greater than said first angular distance. Also, it is beneficial if the assembly includes a fold mirror in an optical path of the light beam between the first and second scan mirrors.
In accordance with this invention, the controller is operatively connected to a memory having stored fonts and timing data as to when to energize and de-energize the assembly to display the image as font characters. The image is preferably a human-readable message.
A method of projecting and displaying an image also forms part of this invention. The method includes the step of (a) generating visible parts of the image by directing a visible light beam toward a viewing surface, and by sweeping the light beam along a plurality of scan lines that extend over the viewing surface; and the step of (b) generating non-visible parts of the image by preventing the directing step at selected positions of the light beam on at least one of the scan lines. Step (a) is performed by energizing a light source, and step (b) is performed by de-energizing the light source. The sweeping step is performed by sweeping the light beam along two mutually orthogonal directions. Step (a) may be performed by energizing a plurality of light sources, and step (b) may be performed by de-energizing the plurality of light sources.
It is also preferable if step (a) and step (b) are performed in a housing having a light-transmissive element through which the swept light beam is directed. Step (a) is performed either by directing the swept light beam at a front surface of a panel mounted on the housing, or by directing the swept light beam at a rear surface of a diffusive screen mounted on the housing.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.